Genome-wide characterization of the role of the KCS gene family in Allium fistulosum L. as regulators of abiotic stress responses

Cuticle wax is a defensive coating on the surfaces of plant tissues that helps shield them from both biotic and abiotic stressors. The 3-ketoacyl-CoA synthase (KCS) enzymes control the rate-limiting step in the synthesis of very-long-chain fatty acids (VLCFAs), thereby regulating wax biosynthesis. In the present study, a genome-wide approach was used to identify 31 members of the KCS gene family in Allium fistulosum that were classified into 9 groups through phylogenetic analysis. These genes were unevenly distributed throughout the A. fistulosum genome, and 7 (AfKCS1, AfKCS2, AfKCS4, AfKCS13, AfKCS17, AfKCS24, and AfKCS28) of them did not harbor any introns. Cis-acting regulatory element analysis revealed that all of these genes were associated with at least one hormone- or stress-responsive element, and heatmap analysis of the expression patterns of these AfKCS genes revealed that they were primarily expressed in the stems and leaf sheaths of A. fistulosum. Eight of these AfKCS genes that were highly expressed in leaf tissue samples harvested from A. fistulosum were further analyzed to detect changes in their expression in response to salt, drought, and low or high temperature stress exposure. All 8 were significantly upregulated in response to salt, low temperature, and high temperature stress, while 4 (AfKCS14, AfKCS15, AfKCS23, AfKCS26) were downregulated in response to drought stress, offering potentially valuable insight into the roles that they play in the context of abiotic stress resistance. Together these findings offer a new foundation for future analysis of the importance of members of the KCS gene family in A. fistulosum play under conditions of abiotic stress and other physiological settings.